Organic semiconductor sensor device

ABSTRACT

Sensor cells are arranged in an array in an organic semiconductor layer. Row and column select circuitry addresses the cells of the array one cell at a time to determine the presence of an object, such as a fingerprint ridge or valley, contacting or proximate to a sensing surface above each cell. Control circuitry can be provided in a companion silicon chip or in a second layer of organic semiconductor material to communicate with the array and an associated system processor. The array of sensor cells can be fabricated using a flexible polymer substrate that is peeled off and disposed of after contacts have been patterned on the organic semiconductor layer. The organic semiconductor layer can be used with a superimposed reactive interface layer to detect specific chemical substances in a test medium.

BACKGROUND OF THE INVENTION

[0001] The present invention relates generally to devices and methods ofdevice fabrication using organic semiconductor materials, and moreparticularly to sensor devices having an organic semiconductor layerthat performs a sensing function.

[0002] It is well known that organic polymeric materials can havecompositions that produce mobile charge carriers, enabling themanufacture of organic semiconductor devices. U.S. Pat. No. 4,222,903discloses a p-type conductivity polyacetylene film that can be dopedwith acceptor dopants to selectively increase its p-type electricalconductivity. A semiconductor material is known as “p-type” conductivitywhen its majority mobile charge carriers are positive charge carrierscalled “holes.” A semiconductor material is known as “n-type”conductivity when its majority mobile charge carriers are negativecharge carriers or “electrons.”

[0003] Inorganic semiconductor materials, principally monolithiccrystalline silicon, are readily fabricated so that both n-type andp-type regions can be formed in a silicon chip. Additionally, inorganicsemiconductor materials have much higher charge carrier mobilities thanorganic semiconductor materials. Such characteristics enable siliconsemiconductor devices to dominate high speed, high density semiconductorapplications using various microscopic elements, like MOSFETs,constructed from n-type and p-type regions in a silicon chip. Yet,organic semiconductor materials have advantages over silicon in theirrelative simplicity of fabrication and lower finished-device cost.Organic semiconductor materials also have certain functional advantagesover silicon-based devices. For example, organic semiconductor devicesdo not require the same rigid, hermetically sealed packages that arecommonly employed with silicon semiconductor devices, since organicsemiconductor devices are less susceptible to damage from exposure tovarious contaminants.

[0004] However, as observed in U.S. Pat. No. 6,252,245, only a limitednumber of organic semiconductor materials have been developed that aren-type. This has restricted the functionality of organic semiconductordevices and limited their practical applications. The fused-ringtetracarboxylic diimide compounds disclosed in U.S. Pat. No. 6,252,245have the potential to enable practical fabrication of both n-channel andp-channel organic thin film transistors (OTFTs), from whichcomplementary OTFT circuits can be constructed. Devices made using suchor similar organic semiconductor technologies can incorporate complexcircuit functionality enabling practical applications that do notrequire the circuit densities and high switching speeds of presentsilicon-based semiconductor devices.

[0005] Additionally, certain applications of organic semiconductortechnology may require only p-type material for the fabrication ofpractical devices. Since the decades old work done with materials likepolyacetylene, described for example in U.S. Pat. No. 4,222,903, higherperformance p-type materials have been disclosed in the art. As anexample, U.S. Pat. No. 5,981,970 discloses the use of pentacene tomanufacture a p-type OTFT with a relatively high field-effect mobility.

[0006] The above-noted U.S. Pat. Nos. 4,222,903; 5,981,970; and6,252,245 are hereby incorporated by reference. These patents are only afew representative examples of an extensive body of knowledge that hasarisen in recent years in the field of organic semiconductor materials.It would be desirable to employ organic semiconductor technology in thedesign of sensor devices for reasons that will become apparent from thefollowing description of the invention.

SUMMARY OF THE INVENTION

[0007] A principal object of the present invention is to provide asensor device fabricated using organic semiconductor material. Thesensor device may have a single sensor element or an array of sensorcells formed in a layer of organic semiconductor material. The layer mayhave a sensing surface on one side and contacts on the opposite side.Means are provided for communicating with the contacts to determine acondition sensed by the sensor element or the conditions sensed by eachof the multiple sensor cells in an array.

[0008] In a preferred implementation, the present invention provides anorganic semiconductor sensor device in which a sensor element has acapacitance that varies with the dimensions of a depletion region. Thecapacitance may vary in response to an object that may be on orproximate to a sensing surface of the sensor element, thereby modulatingthe depletion region.

[0009] In the application in which the sensor element is one of manysuch elements or cells arranged in an array, circuitry is included forselecting one sensor cell of the array at a time, sensing thecapacitance value of the selected sensor cell, and communicating thecapacitance value to a system processor. The system processor receivescapacitance values for all of the sensor cells of the array in a timedsequence and processes the capacitance value data to determinecharacteristics of the object being sensed. This application is ideallysuited for use in a fingerprint detector.

[0010] In a preferred method of fabrication, an organic semiconductorlayer is formed over a flexible polymer substrate. A peelable film isprovided on the top surface of the substrate that supports the organicsemiconductor layer. Contacts are patterned on the exposed surface ofthe organic semiconductor layer, which is then inverted and mounted on asecond permanent substrate. The flexible polymer substrate is thenpeeled off and disposed of leaving a sensing surface of the organicsemiconductor layer exposed.

[0011] In accordance with another application, a reactive interfacelayer can be formed atop the organic semiconductor layer. Chemicalscontained in the reactive interface layer are provided to selectivelyreact to a substance in a test medium contacting the exposed surface ofthe reactive interface layer. A chemical reaction in the reactiveinterface layer creates a change in charge therein that is detected by asensor element in the organic semiconductor layer therebelow. Thisapplication of the invention is ideally suited for use as aninexpensive, disposable, biochemical sensor, such as a blood glucosesensor.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012]FIG. 1 is a schematic cross-section of a sensor element formed ina layer of organic semiconductor material, according to the invention.

[0013]FIG. 2 is a schematic cross-section of a sensor element similar toFIG. 1 in which the sensing element senses the lack of an object incontact with its sensing surface.

[0014]FIG. 3 is a schematic cross-section similar to FIG. 2 but with anobject in contact with the sensing surface of the sensor element showingthe sensor element's response thereto.

[0015]FIG. 4 is a schematic layout in bottom plan view of four sensorelements or cells in a larger array of sensor cells arranged in rows andcolumns.

[0016]FIG. 5 is a schematic cross-section of a portion of FIG. 4 takenalong line 5-5 thereof.

[0017]FIG. 6 is a schematic block diagram showing a sixteen-cell sensorarray according to an embodiment of the invention.

[0018]FIG. 7 is a schematic block diagram showing an array of M rows andN columns of sensor cells of a sensor device according to anotherembodiment of the invention.

[0019]FIG. 8 is a schematic cross-section of a sensor cell of the arrayof FIG. 7 showing a portion of a human finger in contact with the uppersurface of the device with a fingerprint valley above the sensor cell.

[0020]FIG. 9 is a schematic cross-section similar to FIG. 8 but with afingerprint ridge in contact with the upper surface of the device abovethe sensor cell.

[0021]FIG. 10 is a schematic cross-section of a fingerprint sensordevice with an organic semiconductor layer for performing the sensingfunctions and a companion silicon chip for performing the control andcommunications functions through an interconnect circuit provided by anunderlying substrate.

[0022] FIGS. 11-15 are schematic cross-sections showing structures in asequence of steps in the fabrication of a sensor device that may have anarray of sensor cells formed in an organic semiconductor layer.

[0023]FIG. 16 is a schematic cross-section of a fingerprint sensordevice similar to the device of FIG. 10 but with the companion siliconchip mounted beneath the organic semiconductor layer.

[0024]FIG. 17 is a schematic cross-section of a fingerprint sensordevice functionally similar to the view of FIG. 16 but replacing thecompanion silicon chip with a second organic semiconductor layer mountedbeneath the upper organic semiconductor layer.

[0025]FIG. 18 is a schematic cross-section of another embodiment of asensor device that includes an upper reactive interface layer fordetecting chemical substances coming in contact with its surface.

[0026] The cross-sectional views of the figures are partiallycross-hatched. For clarity, cross-hatching has been left off of theorganic semiconductor layers, silicon chips and the reactive interfacelayer in the figures in which they appear.

DETAILED DESCRIPTION OF THE INVENTION

[0027] With reference to FIG. 1, a sensor element in accordance with theinvention is designated generally by reference numeral 10. The sensorelement 10 may have useful applications both as a single such element ina sensing device or as one of many such elements incorporated into anarray forming part of a sensor device. The element 10 includes anorganic semiconductor layer 12 that can comprise any suitable organicsemiconductor material, such as pentacene, that can be prepared withregions of negative and/or positive mobile charges. In its simplestform, the organic semiconductor layer 12 can be chemically structured toprovide a uniform distribution of positive majority mobile positivecharge carriers when the layer 12 is in an unbiased state. The sensorelement 10 can be constructed from organic semiconductor material havingmajority mobile charge carriers of either conductivity type. FIG. 1shows an alternative having a non-uniform distribution of p-typeconductivity material in which a relatively thick upper portion 14extending downward from the upper surface of the organic semiconductorlayer 12 has a light concentration of p-type material, and a relativelythin lower portion 16 along the lower surface of the layer 12 that has aheavy concentration of p-type material to enhance conduction betweencontacts on the lower surface of the layer 12. In the formation of thisnon-uniform p-type alternative, the layer 12 can comprise a composite oftwo or more separately formed sublayers bonded together.

[0028] The layer 12 has an upper surface defining a sensing surface 18that comes into contact with an object or fluid to be sensed or comesinto close proximity to an object to be sensed without direct contact.In a further alternative of the sensor element 10, a thin insulatingfilm (not shown) can be added atop the sensing surface 18, in which casesensing occurs through the overlying thin insulating film. Conductiveplates PI and P2, which are secured to the bottom surface 20 of thelayer 12, serve as contacts for input and output signals applied andsensed at respective terminals 22 and 24. A gate electrode G is alsosecured to the bottom surface 20 intermediate the conductive plates P1and P2. The plates P1 and P2 and gate electrode G may comprise asuitable metal, metal alloy, or other conductive material. Silver is asuitable metal. A switch 26, which preferably is implemented as atransistor, provides a means for selectively connecting the gateelectrode G to a voltage source 28. In the implementation in which thelayer 12 contains positive majority mobile charge carriers, the voltagesource 28 is a positive voltage source. It will be appreciated from thedescription below of various applications of the sensor element 10, thatmore complex structures are contemplated by the invention in whichadditional layers and component parts formed from conductive,semiconductor, or insulating material may be added.

[0029] The sensor element 10 has two modes of operation. The first modeof operation is a conduction mode in which the gate electrode G isunbiased with switch 26 in its open or OFF condition, thus disconnectingthe gate electrode G from the voltage source 28. In this mode, an inputsignal applied to plate P1 can be communicated through the p-typematerial near the bottom surface 20 of the layer 12 to the gateelectrode G and then through the p-type material again to the plate P2.In an application in which the sensor element 10 is one of many suchelements or cells in a two-dimensional array as described below,terminals 22 and 24 can be connected to plates of adjacent sensor cellsto provide a conduction path through the interconnected cells. It willbe appreciated that the plates P 1 and P2 act as capacitor plates aswell as drain and source contacts of a junction field-effect transistor(JFET). The JFET is normally fully ON when the gate is unbiased as shownin FIG. 1.

[0030]FIGS. 2 and 3 show the sensor element 10 operating in the secondof its two modes of operation, which is a sensing mode. In the sensingmode, the switch 26 is in its closed or ON condition causing the gateelectrode G to be biased or energized by the positive voltage source 28.The positive voltage bias on the gate electrode G creates a depletionregion 30 that extends up into the layer 12, driving the JFET transistortoward its pinch-off condition.

[0031] In the example of FIGS. 2 and 3, the sensing element 12 isadapted to sense an object that may be in contact with the sensingsurface 18. When the sensing surface 18 is not contacted by such anobject as shown in FIG. 2, the positive potential on the gate electrodeG creates a depletion region that extends a substantial distance upwardinto the layer 12. An input signal, such as a square-wave pulse, appliedto plate P1 propagates through the undepleted portion of the layer 12above the gate electrode G to the plate P2 by capacitive coupling. Theoutput signal at plate P2 can be quantified to determine that a smallcapacitance condition exists in the sensor element 10, thus indicatingthat an object is not contacting the sensing surface 18.

[0032]FIG. 3 shows the sensor element in the sensing mode with an object32 contacting the sensing surface 18 above the gate electrode G. Forexample, the object 32 can be a single cell of bacteria. The object 32modulates the sensor cell capacitance by attracting positive chargesinto the region of the layer 12 beneath the object causing the heightdimension of the depletion region 30 to contract downward towards thegate electrode G. Thus, a relatively large capacitance is sensed atoutput plate P2 when an input pulse is applied to plate PI and an objectsuch as object 32 is in contact with the sensing surface 18.

[0033]FIGS. 4 and 5 show a portion of a sensor array 40 in which foursensor cells S are shown in two adjacent rows and two adjacent columnsrunning through the array. The array 40 is fabricated in an organicsemiconductor layer 42 (shown in cross-section in FIG. 5), whichpreferably is characterized by a light concentration of p-typeconductivity material uniformly distributed throughout the layer 42. Anupper planar surface 44 and a lower planar surface 46, which are spacedapart in parallel planes, define the thickness of the layer 42. Asubstrate (not shown) supports the layer 12 in a manner described below.A pattern of conductors is provided on the lower surface of the organicsemiconductor layer 42. At each sensor cell location, the pattern ofconductors defines two capacitor plates P1 and P2 with a gate line G_(L)running vertically between the plates. Row line segments R_(L)interconnect the sensor cells S in rows so that input signals can beapplied to each row and communicated along the row (for example, fromleft to right), and then sensed at the right-hand extremity of the array40.

[0034] As an optional feature, a grounded surface grid 48 may beprovided running periodically through the array 40 between the rows andcolumns of cells S, preferably implemented by heavily doped p-type linesselectively introduced into the upper surface 44 of the organicsemiconductor layer 42. When used as a fingerprint sensor, as describedbelow, the grounded surface grid 48 provides a constant referencevoltage at the upper surface 44 to improve the ability to quantify theproximity of the skin of a finger above each of the sensor cells S ofthe array 40. The grounded surface grid 48 optionally can also beconnected to an electrostatic discharge (ESD) protection circuit (notshown).

[0035]FIG. 6 shows a sensor array 60 with sixteen sensor cells S₁₁through S₄₄ arranged in four rows and four columns. Column selecttransistors Q1, Q2, Q3, and Q4 selectively energize the columns, onecolumn at a time, under the control of a control unit 62. An input pulsegenerator 64 sends a pulse signal (such as a square wave pulse)periodically to each of the rows. A line 68 from the control unit 62 tothe pulse generator 64 controls the timing of pulses applied to therows. Row select transistors T1, T2, T3, and T4 selectively interconnectone row at a time with sensing circuitry in the control unit 62, so thatthe input pulse from generator 64 propagates only through one row at atime. Thus, a single sensor cell can be addressed to determine acapacitance value indicative of an object being sensed above the sensorcell, as previously described. A digital value of the sensed capacitancecan be communicated to a system processor (not shown) on a suitable I/Obus from the control unit 62.

[0036] When one of the column select transistors Q₁, Q₂, Q₃, or Q₄ isturned on, a voltage from a voltage source V+ is applied to thatselected column. Load elements R, which may be resistors, cause theselected column to be maintained at a voltage near the positivepotential of the voltage source V+. The load elements have a commonground connection 66, causing the non-selected columns to be dischargedto ground. Thus, using the sensor cell implementation of FIG. 4 in thearray 60 of FIG. 6, the JFET at each cell of a selected column is driventoward pinch-off by the applied voltage V+, while the JFET at each cellof a non-selected column remains in its normally fully ON state.

[0037]FIG. 7 shows an expanded version of the array of FIG. 6. In FIG. 7there are M rows and N columns to provide a rectangular array 70 ofsensor cells S₁₁ through S_(MN). In a case where M=N, the array issquare. For example, in a fingerprint detector a very large number ofsensor cells may be employed in a rectangular or square arrangement. Atypical fingerprint sensor array may have 256 by 256 cells, for example.Each cell may occupy a square area that measures between 20 and 100microns per side.

[0038] A control unit 72 controls the operation of the array 70 and apulse generator 74 that periodically applies input pulse signals to therows of the array 70. Column select circuitry 76 applies a high voltagepotential from a voltage source V+ to one selected column of the array70 at a time, sequencing through the columns under the control of thecontrol unit 72. Row select circuitry 78 selects one row at a time forsensing the capacitance of the sensor cell corresponding to the selectedrow and column. Load elements 80 are provided at the bottom of the array70 to assure that only one selected column at a time is charged to thehigh voltage potential V+, as described above in connection with FIG. 6.

[0039] In a 256-by-256 cell fingerprint detector implemented inaccordance with FIG. 7, it is desirable to include address decodercircuitry (not shown) in the column select circuitry 76 and row selectcircuitry 78 to reduce the number of lines in bus 82 and bus 84connecting the control unit 72 to the respective select circuitry 76,78. In particular, eight address lines in each bus 82 and 84 can encodean address of the column and row of a particular cell of the 65,536cells in the array of 256 by 256 cells. The variable capacitance signalfrom the selected cell of the array 70 is communicated through the rowselect circuitry 78 on line 86 to the control unit 72. The control unit72 may include sensing and amplification circuitry (not shown) thatreceives the signal on line 86. An amplified output corresponding to thesensed variable capacitance of the selected cell may be converted to adigital output by an analog-to-digital converter (not shown) and thentransmitted on input/output bus 88 to a system processor (not shown) forfurther processing or image generation. Such amplification, A/Dconversion, and signal transmission techniques are known in the art offingerprint detectors.

[0040]FIGS. 8 and 9 show the operation of a single sensor element orcell 90 in a fingerprint detector having many such cells in an array.The sensor cell 90 may correspond to the sensor element 10 of FIGS. 1-3described above, and may be operated in an array like the arrays 40 and70 of FIGS. 4 and 7. A portion of a finger 92 is shown above the cell90. In both FIGS. 8 and 9, the gate G is energized with a positivevoltage to produce a depletion region 30 in the organic semiconductorlayer 12 extending up from the lower surface 20 above the gate G. InFIG. 8, a fingerprint valley 94 appears above the sensor cell 90 so thata JFET channel 98 defined above the depletion region 30 is relativelynarrow. In FIG. 9, a fingerprint ridge 96 is in contact with the sensingsurface 18 above the sensor cell 90, modulating the depletion region 30to provide a relatively wide JFET channel 98 between the depletionregion and the upper surface 18. The degree of depletion regionmodulation can be detected by applying a pulse to plate P1 and sensingthe transmission of the pulse at plate P2 to determine the capacitanceof the JFET channel, a channel with a relatively wide height dimensionexhibiting a greater capacitance than a channel with a relatively narrowheight dimension. Since only a single column of the sensor array shownin FIG. 7 is energized at a time, the communication of an input pulsealong a row provides an output that is a function of the capacitancecondition at a single selected sensor cell.

[0041]FIG. 10 shows an implementation of a sensor device 100 in which anorganic semiconductor layer 102 is mounted on a substrate 104 with acompanion silicon chip 106 laterally spaced from the organicsemiconductor layer 102. A support frame 108 is used to secure theperipheral edges of the organic semiconductor layer 102 to the substrate104 and may include connection for the optional grounded surface griddiscussed above with reference to FIGS. 4 and 5. The substrate 104includes an interconnect circuit (not shown) for interconnecting theorganic semiconductor layer 102 with the companion silicon chip 106, andwith contacts 110 at the periphery of the substrate 104 forcommunicating I/O signals with a system processor (not shown). Suchinterconnection techniques are well known in the packaging and PC boardarts. The companion silicon chip 106 performs the complex controlfunctions and communicates with the organic semiconductor layer 102,which includes an array of sensor cells, such as the 256-by-256 cellarray of FIG. 7. The structure of FIG. 10 may be packaged in aprotective housing (not shown), which protects the silicon chip 106 fromdamage while leaving the upper surface of the organic semiconductorlayer 102 exposed to perform its sensing function.

[0042]FIGS. 11 through 15 show a sequence of steps for making a sensordevice having an array of sensor cells formed in an organicsemiconductor layer as previously described. In FIG. 11, a disposable,flexible polymer substrate 120 is provided with a peelable upper surfacefilm 122. Next, as shown in FIG. 12, an organic semiconductor layer 124is formed atop the peelable film 122, the layer 124 having a majorsurface contacting the peelable film and an exposed major surfaceopposite the peelable film. The layer 124 is preferably 20 to 25 micronsthick. The peelable film 122 adheres more strongly to the disposablesubstrate 120 than to the organic semiconductor layer 124. Next, asshown in FIG. 13, a pattern of metal conductors 126 is created atop theorganic semiconductor layer 124. This can be accomplished usingconventional photolithographic techniques or other suitable coating andprinting technologies. Next, as shown in FIG. 14, a permanent substrate128 with interconnect circuitry is provided, including upper surfacecontacts 130 for contacting the organic semiconductor layer conductors126, and metal interconnect lines 132 that may be used to interconnectwith a companion silicon chip or an external system processor (notshown). In FIG. 14, the structure of FIG. 13 has been inverted andmounted on the permanent substrate 128 so that conductors of the metalpattern 126 of the organic semiconductor layer 124 are contacted by thecontacts 130 on the upper surface of the permanent substrate 128. Asshown in FIG. 15, after the structure of FIG. 13 has been inverted andmounted on the permanent substrate 128, the disposable substrate 120with the peelable film 122 adhered thereto is peeled off of the organicsemiconductor layer 124 to expose its sensing surface 134. The structureis then encapsulated or packaged to form the finished sensor device,leaving the sensing surface 134 exposed.

[0043]FIG. 16 shows a device 140 in an alternative arrangement of thedevice 100 of FIG. 10 in which the silicon chip is housed beneath theorganic semiconductor layer. In FIG. 16, an organic semiconductor layer142 is mounted on an upper substrate 144, which in turn is mounted on anannular support 146 that includes an interior cavity that contains acompanion silicon chip 148. These elements are mounted on a lowersubstrate 150, such as a PC board. The upper and lower substrates 144and 150 include conventional interconnect circuitry (not shown).Conductors 152 may be arranged along the interior sidewalls of theannular support 146 to interconnect the upper substrate 144 with thelower substrate 150. Communications with a system processor (not shown)can be made through contacts 154 at the periphery of the lower substrate150.

[0044] As in the embodiment of FIG. 10, the companion silicon chip 148of the embodiment of FIG. 16 can include all of the addressing, controland sensing circuitry for communicating signals to and from the sensorarray that is provided in the organic semiconductor layer 142. Forexample, the column select circuitry, row select circuitry, loadelements, input pulse generator, and control unit shown in FIG. 7 can beincluded in the silicon chip in either embodiment of FIGS. 10 or 16.This simplifies the manufacturing process for making the organicsemiconductor layer, which is much larger in area than the area neededfor a companion silicon chip that is capable of performing theabove-described functions. Compared to conventional silicon-basedfingerprint detectors in which the entire sensor array is fabricated insilicon, the use of a small silicon chip as a companion chip with arelatively large organic semiconductor layer that contains the sensorarray achieves significant cost savings. In addition, the organicsemiconductor layer is more durable than the relatively fragile siliconchips used in prior-art fingerprint detectors. It will be appreciatedthat the devices of FIGS. 10 and 16 can be repaired by replacing theorganic semiconductor layers 102 and 142 in the event that they becomedamaged, salvaging the more expensive companion silicon chips forcontinued use.

[0045]FIG. 17 shows a further alternative embodiment of the presentinvention in which the sensor device is generally designated by numeral160. In FIG. 17, two organic semiconductor layers 162 and 164 areincluded with one mounted atop the other to provide electricalcommunication therebetween. A sensor cell array as previously describedis provided in the upper layer 162. Mounted immediately beneath theupper layer is the lower layer 164 that embodies all of the timing,control, sensing and processor logic of the previously describedcompanion silicon chip. Thus, the fabrication of a more complex organicsemiconductor layer is required for the embodiment of FIG. 17 andrequires advanced processing techniques in which regions of bothnegative (n-type) and positive (p-type) charge carriers can beselectively formed in the organic semiconductor layer 164. Additionally,metal interconnect conductors may be provided on the lower surface ofthe upper layer 162 and on both the upper and lower surfaces of thelower layer 164. The metal interconnect conductors of the lower layer164 can be interconnected with contacts on the surface of a substrate166, which also provides system I/O contacts 168 at its periphery. Aframe 170 secures the organic semiconductor layers 162 and 164 to thesubstrate 166.

[0046]FIG. 18 shows a further alternative embodiment 180 of theinvention in which the embodiment 160 of FIG. 17 has been modified toinclude a reactive interface layer 182 on the upper surface of an upperorganic semiconductor layer 184. In this case, a plurality of sensors,such as the sixteen-cell sensor array of FIG. 6, can be formed in theupper organic semiconductor layer 184 and selectively accessed by acontrol unit and select transistors similar to that as shown in FIG. 6.Alternatively, a single sensor cell can be provided in the upper layer184. The control unit and related functions for interacting with thesensor cell or sensor array in layer 184 can be provided in a lowerorganic semiconductor layer 186. Conductors on the bottom of the lowerorganic semiconductor layer 186 communicate with contacts on a substrate188. The reactive interface layer 182 has an upper surface 190 that canbe exposed to a test medium (gas or liquid) in contact therewith. Thesubstrate 188 communicates with an external system processor (not shown)through contacts 192 at the periphery of the substrate 188.

[0047] The reactive interface layer 182 comprises a polymer that mayinclude a plurality of regions, each region located above acorresponding sensor cell in an array in the upper organic semiconductorlayer 184. Each region in the reactive interface layer 182 includes aspecific chemical that is contained within the polymer of the layer 182,the specific chemical being selectively reactive to a substance in thetest medium contacting the upper surface 190 of the reactive interfacelayer 182. For example, different enzymes can be provided in selectedregions of the reactive interface layer 182. In operation, each enzymecatalyzes a reaction with a specific substance in the test medium. Whenthis reaction occurs, a change in the charge potential at the isolatedregion of the reactive interface layer 182 occurs, which can becapacitively sensed by the sensor cell immediately below that particularregion of the reactive interface layer. In this manner, the presence ofvarious particular substances can be detected in the test medium.

[0048] Alternatively, in the case where a single sensor cell is includedin the upper organic semiconductor layer, a single enzyme, such asglucose oxidase, can be provided in the reactive interface layer 182.When the enzyme reacts with a specific substance, such as glucose, inthe test medium, a change in charge in the reactive interface layer issensed by the sensor cell. This embodiment provides a useful biochemicalsensor device, such as a blood glucose sensor, that can be disposed ofafter a single test procedure.

[0049] Although preferred embodiments have been described in detail, itshould be understood that various changes, substitutions and alterationscan be made therein without departing from the spirit and scope of theinvention as defined by the appended claims.

What is claimed is:
 1. A sensor, comprising: an organic semiconductorlayer having a sensing surface, the layer comprising material havingmajority mobile charge carriers of a first conductivity type distributedthroughout a region beneath the sensing surface; a first conductiveplate spaced from the sensing surface; a second conductive plate spacedfrom the sensing surface and from the first conductive plate; and a gateelectrode interposed between the first and second conductive plates, thegate electrode introducing a depletion region in the organicsemiconductor layer beneath the sensing surface in response to a voltagebias applied to the gate electrode, a dimension of the depletion regionvarying in response to the presence of an object proximate to thesensing surface, the variation in the dimension being detectable bysensing a signal communicated through the organic semiconductor layerbelow the sensing surface.
 2. The sensor of claim 1 wherein the firstconductivity type is p-type characterized by a uniform distribution ofpositive majority mobile charge carriers in an unbiased state.
 3. Thesensor of claim 1 wherein the organic semiconductor layer has anon-uniform distribution of p-type conductivity material, the layerincluding a relatively thick upper portion having a light concentrationof p-type material extending downward from the sensing surface and arelatively thin lower portion having a heavy concentration of p-typematerial extending downward from the relatively thick upper portion to alower surface of the layer opposite from the sensing surface.
 4. Anorganic semiconductor device, comprising: an organic semiconductor layerhaving upper and lower planar surfaces spaced apart in parallel planesdefining the thickness of the layer; and a pattern of conductors on thelower surface defining an array of sensor cells arranged in rows andcolumns, the conductors at each cell location including first and secondplates and a gate between the plates, the gate of each cell introducinga depletion region in the organic semiconductor layer in response to avoltage bias applied to all gates of one selected column, the depletionregion extending upward from the lower surface, a dimension of thedepletion region in the direction perpendicular to the parallel planesvarying in response to the presence of an object proximate to the uppersurface, the degree of variation of the dimension being detectable bysensing a signal communicated through the organic semiconductor layerbelow the upper surface of the layer, the signal being communicatedthrough the cells of one selected row, only one cell of the arraycorresponding to the selected column and selected row being sensed at atime.
 5. The organic semiconductor device of claim 4 wherein the organicsemiconductor layer comprises p-type conductivity material,characterized by a uniform distribution of positive majority mobilecharge carriers above the plates of each sensor cell when the layer isin an unbiased state.
 6. The organic semiconductor device of claim 4further comprising: a control unit; column select circuitry operating inresponse to the control unit for connecting only the cells of theselected column to a voltage source to introduce depletion regions abovethe gates of the cells of the selected column; and row select circuitryoperating in response to the control unit for connecting only theselected row to the control unit for sensing the signal communicatedthrough the selected row.
 7. The organic semiconductor device of claim6, further comprising: a pulse generator connected to the rows operatingunder the control of the control unit for generating the signal that iscommunicated through the selected row; and a load element for eachcolumn connecting the column to a ground connection causing the gates ofthe cells of the non-selected columns to be discharged to ground whilethe gates of the cells of the selected column are energized by thevoltage source.
 8. A fingerprint detector, comprising: an organicsemiconductor layer having an array of sensor cells formed therein, thelayer having an upper sensing surface and conductors on a lower surface;a substrate on which the organic semiconductor layer is mounted, thesubstrate having an upper surface with contacts thereon; and a siliconsemiconductor chip supported proximate to the organic semiconductorlayer and in electrical communication therewith; wherein selectedcontacts on the upper surface of the substrate are connected to theconductors on the lower surface of the organic semiconductor layer. 9.The fingerprint detector of claim 8 wherein the organic semiconductorlayer includes a grounded grid disposed therein at the sensing surface.10. The fingerprint detector of claim 9 further comprising a frame atthe peripheral edges of the organic semiconductor layer for securing thelayer to the substrate and providing a connection to the grid.
 11. Thefingerprint detector of claim 8 wherein the silicon semiconductor chipis mounted on the upper surface of the substrate.
 12. The fingerprintdetector of claim 8 further comprising: a second substrate disposedbeneath the substrate on which the organic semiconductor layer ismounted; and an annular support mounted on the second substrate andsecuring the two substrates together, the annular support having aninterior cavity that contains the silicon semiconductor chip, thesilicon semiconductor chip being mounted on the second substrate beneaththe organic semiconductor layer.
 13. A method of making a sensor device,comprising: providing a flexible polymer substrate; forming a peelablefilm on an upper surface of the flexible polymer substrate; forming anorganic semiconductor layer atop the peelable film, the layer having anexposed major surface opposite the peelable film; creating a pattern ofconductors atop the exposed major surface of the organic semiconductorlayer; providing a permanent substrate with contacts on an upper surfacethereof; mounting the organic semiconductor layer with the flexiblepolymer substrate secured thereto by the peelable film on the permanentsubstrate oriented so that selected conductors of the pattern ofconductors on the organic semiconductor layer make contact with thecontacts on the upper surface of the permanent substrate; and removingthe flexible polymer substrate with the peelable film adhered theretofrom the organic semiconductor layer.
 14. A sensor device, comprising: asubstrate having an upper surface with contacts thereon; a lower organicsemiconductor layer mounted on the upper surface of the substrate andelectrically interconnected therewith, the lower organic semiconductorlayer including regions of n-type and p-type conductivity thereindefining control circuitry; and an upper organic semiconductor layermounted above the lower organic semiconductor layer and electricallyinterconnected therewith, the upper organic semiconductor layerincluding an array of sensor cells therein.
 15. The sensor device ofclaim 14 wherein the upper organic semiconductor layer is characterizedby p-type conductivity material throughout the upper organicsemiconductor layer.
 16. The sensor device of claim 14 wherein the arrayof sensor cells are adapted to sense the presence of the skin of a humanfinger in contact with a sensing surface of the upper organicsemiconductor layer, the sensor cells being capable of distinguishing afingerprint ridge from a fingerprint valley thereabove.
 17. The sensordevice of claim 14 wherein each sensor cell is structured to provide ajunction field-effect transistor thereat, the transistor having sourceand drain contacts and a gate electrode therebetween, the gate electrodebeing selectively energizable to cause the sensor cell to operate in asensing mode when the gate electrode is energized, each sensor cellhaving a JFET channel in the sensing mode, wherein the JFET channel hasa capacitance that varies with the presence or absence of an objectproximate to a surface portion of the upper organic semiconductor layerdirectly above each sensor cell.
 18. A sensor device, comprising: asubstrate having an upper surface with contacts thereon; an organicsemiconductor layer supported above the substrate, the organicsemiconductor layer including a sensor cell therein; and a reactiveinterface layer disposed on the organic semiconductor layer, thereactive interface layer having an exposed upper surface, the reactiveinterface layer comprising a polymer containing a chemical that isselectively reactive to a specific substance in contact with the exposedupper surface; wherein a reaction in the reactive interface layer of thechemical therein with the specific substance is sensed by the sensorcell in the organic semiconductor layer, whereby the sensor device candetect exposure to the specific substance.
 19. The sensor device ofclaim 18 wherein the chemical is an enzyme.
 20. The sensor device ofclaim 19 wherein the enzyme is glucose oxidase and the specificsubstance is glucose.